Problem: $-\dfrac{9}{12} + \dfrac{8}{10} = {?}$
Explanation: $ = - {\dfrac{9 \times 5}{12 \times 5}} + {\dfrac{8 \times 6}{10 \times 6}} $ $ = - {\dfrac{45}{60}} + {\dfrac{48}{60}} $ $ = - \dfrac{{45} + {48}}{60} $ $ = \dfrac{3}{60}$